autotest: Automatically infer HT40+- in HostapConfig

Allow test writers to specify that they want to configure hostapd with a
strict HT40+ configuration, a strict HT40- configuration, or any
supported HT40 configuration depending on what the channel supports.

TEST=All HT40 tests remain passing.  A pending test that only specifies
an HT40 test correctly picks HT40+ vs HT40- depending on the channel
selected.
BUG=None

Change-Id: I4b3b724c23a0e89e38ee5b672be577ffcdda3df3
Reviewed-on: https://chromium-review.googlesource.com/169904
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
Tested-by: Christopher Wiley <wiley@chromium.org>
2 files changed